There are two broad types of devices that are generally sold as RV surge protectors, and they have wildly different capabilities.
One class is just basically a larger version of a surge suppressor power strip such as might be used for home computers. These provide rather limited protection against transient voltage spikes, and nothing more. (Some do also have little test lights to indicate miswired outlets, identical to those in the three light outlet testers you can get.)
The other class is perhaps more properly described as a simple EMS (Electrical management system) and has a contactor controlled by a little computer that monitors the power line and cuts power off if various anomalies are observed, such as low or high line voltage, reversed outlet polarity, disconnected or unbonded ground connections, etc. These generally also have MOVs to protect against voltage spikes.
The latter kind is considerably more expensive but IMHO well worth the extra cost. Protection from low line voltage, in particular, is useful and important for the longevity the air conditioner and some other appliances. Low voltage is not uncommon in campgrounds.